This invention relates to an improvement in shielded wire for use in audio equipment, and of wires having outer conductors such as coaxial cable (shield wire and coaxial cable are hereinafter referred to "shielded wire").
Typical types of the conventional shielded wires are shown in FIGS. 1(a) and 1(b), wherein FIGS. 1(a) and 1(b) show a single core type and double core type shielded wire, respectively.
Reference character C shows a coaxial core which comprises a central conductor 1, a plastic insulation layer 2 made of polyethylene-ethylene copolymer, or foamed materials thereof, and a shield layer 3. The shield layer 3 has a plurality of soft-copper wires or tin plated soft copper wires, each longitudinally disposed about the plastic insulation layer 2.
A ground wire 4 made of soft copper wire or soft copper wire plated with tin is longitudinally spliced along the coaxial core C or is helically wound thereabout with a relatively large pitch. Finally a plastic sheath 5 made of polyethylene or polyvinylchloride is formed by extrusion to cover the coaxial core C and the grounded wire 4.
Such types of shielded wires exhibit desirable electric characteristics, since each of the cores is shielded and the ground wire 4 is closely contacted with the shield layer 3. However, since the shield layer 3 is composed of a plurality of thin lines each longitudinally disposed along the insulating layer, the insulating shielded wire is costly, and long periods of time are required to deal with the thin lines in finishing the end portion of the shielded wire. Therefore, demands have been made for a shielded wire wherein the end portion thereof may be easily constructed.
In order to meet this demand, another type of conventional shielded wire has been provided as shown in FIGS. 2(a) and 2(b), wherein FIGS. 2(a) and 2(b) show single core type, and double core type shielded wires, respectively. In FIGS. 2(a) and 2(b), like parts and components are designated by the same reference numerals as those shown in FIGS. 1(a) and 1(b).
According to these shielded wires, a tubular shield layer 23 is provided. The shielded layer is made of a composite tape, i.e., plastic materials, such as polyethylene-ethylene copolymer, are laminated over an electro-conductive metal tape made of copper or aluminum. The composite tape is longitudinally spliced or wound over the coaxial core and the ground wire to internally position the metal tape. Since the metal tape contacts the ground wire 4, while the laminated plastic tape is externally positioned, the laminated plastic tape is thermally melt-bonded with a plastic sheath 5 during extrusion thereof.
According to these types of shielded wires, since the shield layer 23 is melt-bonded with the plastic sheath 5, the shield layer 23 is easily removed by removing the sheath 5 during the end finishing step. However, complete shielding of each of the conductors is not obtainable and hence the practical application of wires of this type has not been achieved.